1. Field of the Invention
The invention is directed to an improved fuel injection apparatus for internal combustion engines having a fuel pump for each engine cylinder.
2. Description of the Prior Art
One fuel injection apparatus of the type with which this invention is concerned is known from the literature, for instance from the textbook entitled Dieselmotor-Management [Diesel Engine Management], 2nd Ed., Verlag Vieweg, page 299. This known fuel injection apparatus, for each cylinder of the engine, has one fuel pump, one fuel injection valve, and one line connecting the fuel injection valve to the fuel pump. The fuel pump has a pump piston, driven in a reciprocating motion, that defines a pump work chamber. Near the fuel pump is a control valve, by which a communication of the pump work chamber with a relief chamber is controlled. The fuel injection valve has an injection valve member, by which at least one injection opening is controlled and which is movable in the opening direction counter to a closing force by means of the pressure generated in the pump work chamber by the fuel pump. By means of the control valve, the instant and duration of opening of the fuel injection valve can be controlled; the instant of opening is determined by providing that the pump work chamber is disconnected from the relief chamber by the control valve, and thus the high pressure generated by the fuel pump in the pump work chamber is operative. For closure of the fuel injection valve, the pump work chamber of the fuel pump is made to communicate with the relief chamber by the control valve, so that no further high pressure is operative in the pump work chamber, and the fuel injection valve is closed by the closing force acting on the injection valve member. The control valve is-disconnected by means of the line and is located relatively far from the fuel injection valve, so that when the communication of the pump work chamber with the relief chamber is opened by the control valve, the pressure at the fuel injection valve drops only in delayed fashion, and accordingly the fuel injection valve closes only with a delay, so that the instant and duration of opening of the fuel injection valve can be determined only imprecisely. A brief opening and closure of the fuel injection valve for a preinjection and postinjection that are chronologically offset from a main injection is thus feasible only with difficulty.
The fuel injection apparatus of the invention has the advantage over the prior art that by means of a second control valve, a fast, undelayed closure of the fuel injection valve is made possible, as is necessary in particular to make a preinjection and postinjection that are chronologically offset from a main injection possible. To close the fuel injection valve, a high pressure is established by the second control valve in the pressure chamber of the fuel injection valve, and by this pressure the injection valve member is urged in the closing direction.